Re: [PATCH v2 2/4] mfd: Add RZ/V2M PWC core driver

Geert Uytterhoeven
2023-01-03T12:10:47Z

Hi Fabrizio,

On Tue, Jan 3, 2023 at 1:05 PM Fabrizio Castro
<fabrizio.castro.jz@renesas.com> wrote:
> > From: Geert Uytterhoeven <geert@linux-m68k.org>
> > On Wed, Dec 21, 2022 at 10:09 PM Fabrizio Castro
> > <fabrizio.castro.jz@renesas.com> wrote:
> > > The External Power Sequence Controller (PWC) IP (found in the
> > > RZ/V2M SoC) is a controller for external power supplies (regulators
> > > and power switches), and it supports the following features: it
> > > generates a power on/off sequence for external power supplies,
> > > it generates an on/off sequence for the LPDDR4 core power supply
> > > (LPVDD), it comes with General-Purpose Outputs, and it processes
> > > key input signals.
> >
> > Thanks for your patch!
> >
> > > The PWC is basically a Multi-Function Device (MFD), its software
> > > support comes with a core driver, and specialized drivers for
> > > its specific features.
> >
> > I have to admit I'm not such a big fan of MFD. In this driver,
> > you are not even sharing resources in the MFD cells, just the mapped
> > register base. So I think you can easily save +100 LoC and reduce
> > maintenance synchronization overhead across subsystems by just having
> > a single non-MFD driver instead.
> >
> > Did you pick MFD because the PWC poweroff feature depends on board
> > wiring, and thus is optional?
>
> I am not a big fan of MFD, either.
> I picked MFD because we were not 100% sure of what the IP could do
> when we started working on it.
> I have received more information regarding the IP now (which I don't
> have the liberty to discuss), I am still not 100% sure that's all
> of it, but basically its support may require expansion later on.
>
> I liked the solution based on syscon and simple-mfd for several reasons,
> but having dropped syscon and simple-mfd due to issues with the dt-bindings
> I have moved on with a core driver to instantiate the required SW support.
> We could of course move to a unified driver if that makes more sense?
> If we were to move to unified driver, under which directory would you
> suggest we put it?

As the GPIO part is larger than the poweroff part, I would put it under
drivers/gpio/. Although drivers/soc/renesas/ could be an option, too.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds